The invention relates to a process for adjusting the strain of a strained layer on the surface or inside a substrate made of a semiconductor material. For example, the invention relates to a process for locally adjusting the strain in one or several layers on a substrate made of a semiconductor material.
The invention also relates to a process of adjusting the strain on a part of the surface or on the entire surface of a substrate made of a semiconductor material with a surface or buried strained layer. In general, the invention is applicable to all types of strained layers on a substrate made of a semiconductor material and with a non-homogenous strain, on the surface of the layer or within the depth of this layer.
The process according to the invention is particularly suitable for making a local adjustment to the strain in a layer obtained by epitaxy on a substrate. The invention also relates to a strained layer on a substrate made of a semiconductor material having less defects by being obtained by the process according to the invention. Finally, the invention relates to a wafer made of a semiconductor material comprising at least one such layer.
The use of a strained layer on a substrate is particularly attractive because it can increase the mobility of charge carriers within semiconductor structures. A person skilled in the art will be familiar with several techniques and processes for creating a strain within a layer on a substrate. For example, a silicon layer may be strained by epitaxy on a substrate for which the elementary mesh parameter in the epitaxy plan is not the same as the mesh parameter for silicon. Such a process is better known under the name of pseudomorphic epitaxy. With this process, the surface of the strained layer is analyzed to show that there is a non-homogeneity in the strain of the order of 1% of the maximum strain, measured between the centre and the edge of the substrate.
With this process, the sources of this non-homogeneity of the strain in the substrate layer may be:                a non-homogeneity in the composition of the alloy (for example SiGe) used in the pseudo-substrate obtained by epitaxy on the solid substrate (homogeneity of the temperature on the pseudo-substrate during epitaxy, constant gas flows in the reactor); or        relaxation of strain due to heat treatments (thermal oxidation, post-epitaxy heat treatments, etc.).        
Thus, the precision of existing processes for obtaining the required strain in the layer concerned is limited, and it would be advantageous to improve this precision to achieve good mobility of charges within the strained layer.
Obviously, existing processes could be improved by carrying out more frequent checks of the temperature of heating lamps and gas flows in the reactor, and the precision of these installations could also be improved. Another possibility is to provide an additional treatment process carried out after a known process for producing a strained layer. The purpose of this invention is to provide such a process.